Kathy from Hampstead writes: My daughter, aged 26 ,has almost qualified as an architect. She is a beautiful girl and boys have flocked around her since she was a teenager, but she is also level-headed.

She was engaged to a boy of whom I was very fond, not least because his mother and I are old school-friends. However they rowed over something rather silly, in fact his refusal to attend a family simchah with her, and things escalated. She broke off the engagement and returned his ring. Subsequently she has met someone else whom she prefers and whom she is dating.

However her ex-fiance is now behaving in a wild and frightening way. He bombards her daily with letters, texts and emails (she no longer accepts his calls), begging her to return. He sends flowers continually to her at work, he lurks around the tube station waiting for her to arrive, and last week he came to her flat late at night. She would not let him in. He then broke a pane of glass. The tone of his messages varies from the self-pitying, cannot-live-without-her-and-wants-to-end-it-all type, to the menacing, if-he-can't-have-her-no-one-else-will type. I have spoken firmly to his mother, who begs me not to harm his career as a solicitor. My son who is very tough has warned him in less polite terms to no avail. We are reluctant to go to the police but are now at our wits end. Can you advise?

Kathy, I am constantly amazed at the extent to which our courts are filled with the consequences of unrequited love, in one form or another. Nor is such behaviour limited to the male sex. I once read that medical research shows romantic infatuation can bring about measurable changes in the brain's chemistry. Apparently these rarely last beyond a year. The problem is not new. As Polonius says of Hamlet, "He is far gone, far gone. And truly in my youth I suffered much extremity for love, very near this."

It seems to me, realistically, you have three options. One is to do nothing. I hope I am not being alarmist when I say that this could possibly prove dangerous. The other two options both involve invoking the Protection from Harassment Act 1997.

This useful Act made it a criminal offence to pursue a course of conduct which amounts to harassment of another person, punishable in the Magistrates Court with up to six months imprisonment in the worst of cases - which, of course, this is far from being yet. Conduct amounts to harassment "if a reasonable person in possession of the same information would think the course of conduct amounted to harassment", and includes "alarming another person, or causing distress". To invoke the criminal jurisdiction, your daughter would first need to complain to the police.

The police also operate an informal procedure, whereby in a less serious case, such as this currently is, they can issue a written notice, which warns him that an allegation of harassment has been made against him, and that if he continues, they will prosecute. It is a sort of "yellow card" like in football. It does not of itself constitute a conviction or admission. Usually it has the desired effect.

The Act also provides for a civil remedy, whereby your daughter could seek an injunction from the County Court ordering him to desist from his behaviour, and/or damages for her anxiety. If he disobeyed that injunction, she could return to the court and apply for a warrant for his arrest.

I think the kinder and more anonymous route, however, in view of past happier days, would be to instruct a solicitor to write a warning letter, saying that if he does not cease all attempts to communicate with her, she will seek a civil injunction and damages under the Act. Hopefully this will be effective.

There is in my experience a small hardcore of individuals who have a personality flaw which prevents them from desisting, and who are capable of extreme acts, If he does not come quickly to his senses thereafter, you must then not hesitate to invoke the full force of the law against him.

Better that, than to risk the safety of your daughter to whom your first loyalty lies, even at the risk of losing your old school-friend.